1. Field of the Invention
The present invention relates to a hub member for a rigid or flexible medical conduit.
2. Description of Related Art
As used in the present application, the term "medical conduit" includes metal or plastic cannulas and flexible catheters or the like that are inserted for withdrawing blood or for supplying blood, infusion liquids or medicaments into the vessels of a patient. When the tip of the conduit enters the vessel, blood will flow back and will emerge from most of the known hub members. This should be prevented, due to the danger of the transmission of contagious diseases through the blood. Also, when replacing a continuing conduit by pulling the connecting member off the housing of the hub member, the same will be open and blood may flow therefrom. In a case in which the patient is unfavorably positioned, air may enter the venous system and cause air embolism.
In an attempt to remedy these deficiencies, a hub member with a valve device has been provided (German Patent 28 17 102). In this known device a disc of elastomeric material having a central slit therein is held in a radially extending groove in the wall of the chamber of the housing. Further, the housing contains an adjusting member in the form of a conical sleeve member which is advanced by the pressure of a connecting member; e.g. the hub of a steel cannula, insertable into an insertion opening of the housing, and which in this advanced position presses against the disc and penetrates the disc at least partly to open the slit.
In the case of this known device, the closure is of doubtful reliability after the steel cannula has been withdrawn, since it relies on the inherent resilience of the disc material which will deteriorate due to fatigue of the material. This is particularly so when the device is delivered as a ready for use set in which the smooth edges of the slit in the prestressed disc (which form lips) are deformed over a long time by a steel cannula. For this reason, it is possible that the deformed edges of the slit will not only refuse to sealingly close when the steel cannula is extracted, but they may even leave an open hole through which blood may ooze back.
In order to keep the size of this hole at a minimum, steel cannulas of a larger diameter have been provided in practice with a constriction arranged in the region of the elastomeric disc in the hub member. However, this constriction can only be provided with considerable production efforts. Moreover, the constriction forms a throttle point inside the cannula, so that tissue particles cut out when puncturing a tissue may get stuck at the throttle point and a successful puncture may not be indicated by outflowing blood. Therefore, the user may unnecessarily puncture the vessel several times, causing an inappropriate stress on the patient.
A further known puncturing and insertion device has a valve means with a resilient cup-shaped hollow cylinder, the bottom portion of which is slit (German Patent 31 47 609). In this known device an adjusting member axially displaceable in the chamber of the housing of the hub member and shaped as a jacket open at both ends serves to bias the bottom portion of the stationary cup-shaped hollow cylinder by radial pressure. Prior to use of the device, the inner end of the jacket only encloses the distal open end of the hollow cylinder so that its opposite bottom member is unstressed during storage time and no deformations will occur at the sealing lips that might lead to leakages. A connecting member (e.g. a cannula hub) is inserted in the outer end of the jacket facing the user. The connecting member, when being advanced axially for preparing the cannula tip for the puncture, pushes the inner jacket end entirely over the hollow cylinder and presses the bottom portion radially. In this position, the jacket engages in the housing. This results in the lips of the slit in the bottom portion being permanently pressed together, there being no possibility to relieve the lips. In order to be able, after the removal of the puncturing cannula, to push a highly flexible catheter hose through the closed lips of the radially biased bottom portion or to be able to open the lips by the weak pressure of a fluid flow, the bottom of the hollow cylinder must be very thin and yielding. In such a case, there is a danger that the slit will also open upon a weak pressure of the blood flow and that the valve will not act as a nonreturn valve. Depending on the storage time of a catheter hose, the thin lips at the biased bottom portion deform because of fatigue so that also in this valve device deformation will cause a hole that cannot be closed. In both of the known valve devices of hub members described above, the necessary additional adjusting member increases the production costs of the hub member.
It is an object of the present invention to improve a valve device of the above-mentioned type such that the slit bottom portion of the resilient hollow cylinder can be easily opened in the direction of insertion, while reliably sealing in the reflux direction.